Abstract

Although long considered a promising treatment option for type 1 diabetes, pancreatic islet cell transformation has been hindered by immune system rejection of engrafted tissue. The identification of pathways that regulate post-transplant detrimental inflammatory events would improve management and outcome of transplanted patients. Here, we found that CXCR1/2 chemokine receptors and their ligands are crucial negative determinants for islet survival after transplantation. Pancreatic islets released abundant CXCR1/2 ligands (CXCL1 and CXCL8). Accordingly, intrahepatic CXCL1 and circulating CXCL1 and CXCL8 were strongly induced shortly after islet infusion. Genetic and pharmacological blockade of the CXCL1-CXCR1/2 axis in mice improved intrahepatic islet engraftment and reduced intrahepatic recruitment of polymorphonuclear leukocytes and NKT cells after islet infusion. In humans, the CXCR1/2 allosteric inhibitor reparixin improved outcome in a phase 2 randomized, open-label pilot study with a single infusion of allogeneic islets. These findings indicate that the CXCR1/2-mediated pathway is a regulator of islet damage and should be a target for intervention to improve the efficacy of transplantation.

Introduction

Achieving long-lasting insulin independence after portal vein islet transplantation has improved, but remains challenging. Nonspecific immune activation (1–6), along with preexisting and transplant-induced auto- and allospecific immune responses (7–9), are components affecting outcome; these are not fully suppressed by ongoing protocols of generalized immunosuppression. Increasing general immunosuppression potency is not ideal because of side effects. Consequently, the development of novel protocols that specifically target proinflammatory immune cell compartments that impede islet function and survival is compelling.

Results and Discussion

The CXCL1-CXCR1/2 axis is a therapeutic target for improving pancreatic islet engraftment.

CXCL1 was quantitatively the most relevant inflammatory factor released in culture by mouse islets, both in basal conditions and after IL-1β exposure (Supplemental Figure 1A; supplemental material available online with this article; doi:
10.1172/JCI63089DS1). Accordingly, serum CXCL1 concentrations were increased 24 hours after islet infusion into the portal vein (Supplemental Figure 1B), and intrahepatic CXCL1 mRNA expression was strongly increased 4 hours after islet transplantation (>100-fold; Supplemental Figure 1C). CXCL1 signals through the chemokine receptor CXCR2 (10). To investigate the effects of activating the CXCL1-CXCR2 axis in islet engraftment, Cxcr2–/– and Cxcr2+/+ alloxan-induced severely diabetic BALB-c mice were intrahepatically transplanted with Cxcr2+/+ syngeneic islets. The probability and median time to reach euglycemia were 62.5% and 4 days, respectively, for Cxcr2+/+ recipients, compared with 100% and 1 day for Cxcr2–/– recipients (P = 0.03; Figure ​Figure1A).1A). The genetically targeted mouse model has some limitations, which include a type 2 inflammatory tendency of the BALB-c mouse (11) and the possible redundancy caused by the binding of CXCL1 to the second recently described murine receptor, CXCR1 (12). We therefore studied the effect of pharmacologic blockade of both CXCR1 and CXCR2 on syngeneic islet engraftment using the type 1 inflammatory-prone C57BL/6 mouse as a recipient. Recipient mice were treated with reparixin, a specific noncompetitive allosteric inhibitor of CXCR1 and CXCR2 (13). Islet engraftment was improved in reparixin- versus vehicle-treated mice when either 150 islet equivalents (IEQs; euglycemia probability, 84% vs. 50%; median time to euglycemia, 7 vs. 21 days; P = 0.04) or 250 IEQs (euglycemia probability, 100% vs. 57%; median time to glycemia, 1 vs. 50 days; P = 0.002) were used for transplant (Figure ​(Figure11A).

Among intrahepatic leukocyte (IHL) populations, CXCR2 was expressed on all polymorphonuclear leukocytes (PMNs; Gr1+CD11b+Ly6C–; 97 ± 1%) and on a subpopulation of NKT cells (NK1.1+CD3+; 25 ± 6%) (Figure ​(Figure1B).1B). Both cell populations increased markedly in the livers of mice transplanted intrahepatically with syngeneic or allogeneic islets, and treatment of mice with the CXCR1/2 inhibitor significantly inhibited this rise (Figure ​(Figure1C1C and Supplemental Table 1). Other IHL populations were only marginally affected by reparixin treatment (data not shown). The identification of a targetable pathway able to prevent the recruitment of both these cells is an important finding. PMNs are the predominant cell type infiltrating the islets in experimental models (14), and a vicious cycle mediated by NKT and PMN IFN-γ–based cross-talk was recently demonstrated to be harmful to transplanted islets (15). Concordantly, NKT cell inhibition or deletion improves engraftment and delays islet rejection (1, 2, 15).

Inflammatory status before and after allogeneic islet transplantation in patients with type 1 diabetes.

The findings in mouse and humans led to a phase 2 randomized, open-label pilot study to assess the efficacy and safety of CXCR1/2 inhibition after single-infusion islet transplantation. Inclusion criteria restricted enrollment to patients expected to receive an islet mass in the lower range of the currently accepted transplantable islet amount. Patients were placed on an immunosuppression regimen consisting of induction with ATG and maintenance immunosuppression with FK506 and MMF. Patients were randomly assigned to receive either no additional experimental intervention or CXCR1/2 inhibitor reparixin treatment (2.772 mg/kg BW/h i.v. continuous infusion for 7 days starting from day –1). Initially, 7 consecutive patients were enrolled, with randomization to reparixin treatment in 4 patients (Pt2, Pt3, Pt5, and Pt7; see Supplemental Table 2 and Table ​Table11 for islet and patient characteristics). No reparixin-related adverse events were reported in these patients. None of the patients in the control group expressed β cell function 1 month after transplant (no decrease in insulin requirement coupled with C-peptide levels less than 0.09 ng/ml), and all were withdrawn as a result of graft loss. In contrast, patients treated with reparixin experienced improved transplant outcome, as measured by glycemic control, decreased insulin requirement, and appearance of detectable levels of C-peptide well above 0.3 ng/ml. Fasting C-peptide, reduction of insulin requirement, stimulated C-peptide (evaluated as peak and area under the curve response derived from the 2-hour mixed-meal tolerance test; ref. 16), and islet estimated function (17) were all significantly higher in the reparixin group than in controls (Figure ​(Figure3).3). Based on these results, the ethical review board recommended protocol amendment allowing randomization to the reparixin treatment group only and to allow patients with a functioning graft to receive a second islet infusion. 2 additional patients (Pt8 and Pt9) received islets with reparixin treatment. Pt8 demonstrated excellent islet function (Figure ​(Figure3),3), and Pt9 did not comply with oral immunosuppression treatment and dropped out of the study. The one reparixin-treated patient who did not have markedly improved transplant outcome, Pt7, had a 10-fold increase in GAD autoantibody titer soon after transplant. Pt2, Pt3, and Pt5 from the initial reparixin treatment group received a second islet infusion, and Pt2 and Pt3 achieved insulin independence (total infused, 7,589 and 8,888 IEQ/kg, respectively).

Characteristics of recipients in the reparixin islet transplant trial: first infusion

With the exception of selective CCR5 antagonists for HIV, our results represent the first clinical evidence to our knowledge that chemokine receptor blockade may have therapeutic benefit. Although the numbers in the trial were small, we demonstrated that an important cause of transplanted islet dysfunction in humans was nonspecific inflammation mediated by CXCR1/2 receptor, which is inadequately inhibited by ongoing protocols of generalized immunosuppression. Collectively, the findings suggest a novel approach to prevent early loss of transplanted islets. A phase 3 multicenter, randomized, double-blind, parallel-assignment trial has commenced to confirm the results of this pilot study. We further suggest that targeting the CXCR1/2 pathway may be therapeutically relevant for the preservation of islet function in new-onset type 1 diabetes.

Methods

Mice.

Male C57BL/6 and BALB-c mice were purchased from Charles River Laboratories. Cxcr2–/– mice on BALB-c background [strain C129S2 (B6)-IL8RB] were provided by Dompè spa. Pancreatic islets were isolated and transplanted via the portal vein as previously described (11). Reparixin was provided by Dompè spa and administered by s.c. continuous infusion (Alzet Osmotic pump; Alza Corp.) starting from day –1 up to day 6 after islet transplantation at a dose of 5.4 mg/kg/h. Recipient mice were rendered diabetic with i.v. alloxan injection (60–75 mg/kg; Sigma-Aldrich). Blood glucose measurements were performed using a Glucometer Elite (Bayer Canada). Euglycemia was defined as nonfasting blood glucose concentrations of less than 200 mg/dl in 2 consecutive measurements. For evaluation of intrahepatic leukocytes, single-cell suspensions were prepared from 2 liver lobes of known weight, and analysis of IHL population was performed by flow cytometry. Cells were stained with FITC-, PE-, or allophycocyanin-labeled (APC-labeled) anti-CD4, anti-CD8, anti-CD3, anti-CD19, anti-TCRb, anti-NK1.1, anti-CD11, anti–Gr-1, anti-CD11b, anti-Ly6C, or anti-CD11c Abs (BD Biosciences — Pharmingen).

Statistics.

Analysis of data was performed using the SPSS statistical package for Windows (SPSS Inc.). A 2-tailed P value less than 0.05 was considered significant.

Study approval.

All patients gave informed consent for the investigations. The ethical committee of the Istituto Scientifico Ospedale San Raffaele approved the islet transplant protocols and investigations. Investigations were carried out in accordance with the principles of the Declaration of Helsinki, as revised in 2000. All mouse experiments were in accordance with protocols approved by the Animal Care and Use Committee of San Raffaele Scientific Institute.

Supplementary Material

Acknowledgments

This work was supported by the EU (HEALTH-F5-2009-241883-Beta­CellTherapy), the Juvenile Diabetes Research Foundation (JDRF grants 6-2006-1098, 31-2008-416, and 4-2001-434), and a research grant from Dompé spa to L. Piemonti (HSR-DRI, Milan). C. Antonio is enrolled as a PhD student in the Department of Surgery at University of Pavia. E. Cantarelli conducted this study as partial fulfillment of her PhD in Molecular Medicine, Program in Basic and Applied Immunology, San Raffaele University. The phase 2 clinical trial is sponsored by Dompé spa.

Footnotes

Conflict of interest: Lorenzo Piemonti’s research was funded by Dompè Spa in the fiscal year preceding the date of the original submission.